This invention relates to an RF tag reading method and apparatus for supplying a radio-information storage medium (an RF tag), which is equipped with an antenna and a semiconductor integrated circuit, with power by electromagnetic coupling and receiving a signal that is transmitted from the RF tag, thereby recognizing the tag and reading information that has been stored on the tag. More particularly, the invention relates to a tag reading method and apparatus for supplying power to a plurality of RF tags that overlap in the zone of supplied power and reading information from the tags.
A method employed widely in the prior art to manage individual items of product information in the distribution and transport industries involves printing or affixing a bar code on the product itself or on the box of the product and reading the bar code by a bar code reader. With a bar code processing method of this kind, however, the bar code reader must be brought into contact with the bar code when the bar code is read. This reading operation is a troublesome one. Another problem with the conventional bar code processing method is that new information cannot be added to a bar code per se and information contained by the bar code cannot be updated.
As a result, there is growing demand for systems in which an RF tag instead of a bar code is affixed to a product or the like and information relating to the product is read without contact by wireless means (electromagnetic coupling), and such systems are currently being put to practical use. An RF tag is a device in which a function for radio communication of information has been added to the functions of an IC card. The RF tag is equipped with a non-volatile memory that is capable of recording information but does not possess a battery (power source). As a consequence, when a tag reading apparatus contactlessly reads information from the memory of the RF tag, the RF tag is supplied with power by electromagnetic waves so that information can be read from the memory. In accordance with such an RF tag, operability can be improved by a wide margin. Moreover, by using an authentication function and techniques such as encryption in combination with an RF tag, outstanding security can be achieved.
FIG. 38 is a diagram useful in describing an RF tag. A reading apparatus 1 transmits a radio signal (electromagnetic waves), which has been modulated by transmit data, to an RF tag 3 from an antenna 2. The RF tag 3 has an antenna 3a that inputs the receive signal to a rectifying circuit 3b and modem circuit 3c. The rectifying circuit 3b operates as a power source by converting the radio signal to a DC voltage and supplying the DC voltage to the modem circuit 3c and to a logic circuit 3d. The modem circuit 3c demodulates control data, which has been sent from the reading apparatus 1, and inputs the control data to the logic circuit 3d. The latter executes logical processing in accordance with the control data (commands), reads information that has been stored in an internal memory and inputs the information to the modem circuit 3c. The latter modulates a carrier wave using the information that has entered from the logic circuit 3d and transmits the modulated signal from the antenna 3a to the reading apparatus 1.
In a case where a plurality of RF tags are present within the zone of the supplied power, the reading apparatus 1 is capable of reading information from each RF tag in accordance with an anti-collision protocol. Various schemes have been proposed in regard to anti-collision protocols. For example, one is described in the specification of ISO 18000.
Even if a plurality of RF tags are located within the zone supplied with power, no problems arise so long as the RF tags do not overlap one another. Frequently, however, there are cases where articles overlap one another, as at the site of manufacture, in an automated warehouse or at the place of sales, and information is read from all tags at one time. If articles thus overlap one another, then a plurality of RF tags also will overlap. A situation arises in which RF tags near the reading apparatus receive power from the reading apparatus while RF tags that are more distant do not receive power satisfactorily.
Further, an RF tag is equipped with an antenna whose characteristic matches the radio frequency in order to receive power from the reading apparatus efficiently and communicate with the reading apparatus properly. However, when a plurality of RF tags are in close proximity to one another, the antenna characteristic shifts from the radio frequency owing to interaction among the tag antennas. As a result, the power supplied diminishes even further and does not attain a value at which more distant RF tags can operate. This means that information cannot be read from these tags.
A proposed method of solving this problem is to prepare a tag case and move the antenna within the tag case to thereby avoid overlap of the antennas. This makes it easy even for tags in back to receive power. (For example, see the specification of JP 2000-331136A).
FIGS. 39A, 39B are diagrams useful in describing an RF tag according to the prior art. The RF tag 5 includes an inlet 5c (the portion encircled by the dashed line) seated within a tag case 6a. The inlet 5c comprises a coil-shaped transceive antenna 5a and an electronic part 5b mounted on the surface of a board and connected to the transceive antenna 5a. The tag case 6a has an internally provided inlet accommodating portion 6b and is formed in such a manner that the internal diameter B thereof is sufficiently larger than diameter C of the inlet 5c (i.e., B>C). By accommodating the inlet 5c in the inlet accommodating portion 6b without fixing it, the inlet 5c received within the inlet accommodating portion 6b is accommodated slidably without the position thereof being specified. By virtue of this arrangement, the transceive antennas can be staggered so as to overlap partially rather than completely even if a plurality of the RF tags 5 are read or written to in a stacked condition. As a result, power is fed to the transceive antennas of all RF tags, thereby making it possible to read information from and write information to each of the RF tags.
A problem which arises with the above technique, however, is that since the conventional RF tag has a tag case, the above-described technique cannot be applied to an article to which it is difficult to attach the tag case.